1. Field of the Invention
The present invention relates to an optical drive having a plurality of light sources, and more particularly, to an apparatus and method for detecting beam power generated by a plurality of light sources using a single device.
2. Description of the Related Art
It is possible to record or reproduce data on an optical medium using an optical drive having a plurality of light sources with different wavelengths. To record data on or reproduce data from two different discs, e.g., a disc classified as a compact disc (CD) and a disc classified as a digital versatile disc (DVD), in one optical drive, the optical drive is required to have separate light sources for a CD and a DVD. This is because the standard wavelengths required for recording data on or reproducing data from CDs and DVDs are different.
The output of light sources typically become reduced when the temperature rises in the optical drive. To solve this problem; the optical drives include an auto power control (APC) function of monitoring the beam power generated by a each light source to control the power of the light sources automatically.
The optical drive, however, monitors the beam power using one device. In other words, beam powers generated by the plurality of light sources are detected via one monitor photo diode (MPD). Therefore, the amplification gain (or sensitivity) of the MPD is set to be uniform for the plurality of light sources. However, if there are any differences between maximum beam powers generated by the plurality of light sources, it is difficult to ensure a dynamic range for detecting the beam power generated by each light source. For this reason, it is impossible to realize an APC that consistently provides the light power required.
FIG. 1 is an illustration explaining a relationship between the beam power required in an optical drive having light sources for a CD and a DVD and the beam power in the optical drive detected by MPD. Referring to FIG. 1, the maximum beam power from the light source for a CD appears to be twice as large as that from the light source for a DVD, with the amplification gain of the MPD being the same for both light sources. In this case, the light source for a CD has a sufficient dynamic range for detecting the beam power, whereas the light source for a DVD has only half of the dynamic range required. To solve this problem, it has been suggested that monitor photo diodes (MPDs) that have amplification gains corresponding to the respective light sources be attached to an optical drive. However, a disadvantage of this technique is that the optical drive must be larger to encompass the multiple MPDs. Further, an installation of the multiple MPDs increases manufacturing costs.